Currently, apparatuses which form images according to an electrophotography system have been prevalently used. For example, laser beam printers which form (print) images on cut sheets, OHP sheets, and the like on the basis of an image signal sent from a host apparatus such as a computer or the like have prevailed, and some models of such printers have a staple function of stapling a set (bundle) of sheets (recording media) on which images are formed.
Such staple function is normally provided by a sheet processing apparatus which is connected to an image processing apparatus upon use, and Japanese Patent Laid-Open No. 11-322181 describes such sheet processing apparatus.
A conventional image forming apparatus and a conventional sheet processing apparatus will be described below with reference to FIGS. 10 to 15. FIG. 10 is a schematic sectional view showing the structure of an image forming apparatus, FIG. 11 is a view for explaining a scanner unit, FIG. 12 is a schematic sectional view showing the structure of a sheet processing apparatus, FIG. 13 is a top view of the sheet processing apparatus, FIG. 14 is a block diagram showing electrical connections between the image forming apparatus and sheet processing apparatus, and FIG. 15 is a graph schematically showing a change in consumption current in the sheet processing apparatus.
The image forming operation of an image forming apparatus 301 of this prior art will be described below mainly with reference to FIGS. 10 and 11. Reference numeral 101 denotes an image signal (VDO signal), which is input to a laser unit 102. Reference numeral 103 denotes a laser beam which is ON/OFF-modulated by the laser unit 102. Reference numeral 104 denotes a scanner motor, which steadily rotates a rotary polygonal mirror 105. Reference numeral 106 denotes an imaging lens which forms a focal point of a laser beam 107 deflected by the polygonal mirror on a photosensitive drum 108 as a surface to be scanned.
Therefore, the laser beam 107 modulated based on the image signal 101 is horizontally scanned (in the main scan direction) on the photosensitive drum 108. Reference numeral 109 denotes a beam detection port which fetches the beam via a slit-like entrance port. The laser beam which has entered via this entrance port is guided to a photoelectric conversion element 111 via an optical fiber 110. The laser beam which is converted into an electrical signal by the photoelectric conversion element 111 is amplified by an amplifier circuit (not shown) to obtain a horizontal sync signal.
A latent image formed on the photosensitive drum 108 is visualized by a developer 123 to obtain a toner image, which is transferred onto a transfer sheet 112 by a transfer roller 120.
Reference numeral 131 denotes a paper cassette which feeds one type of standard-size transfer sheets of a size selected from an A4 size, LETTER size, and the like.
A single-sided print operation on the transfer sheet 112 fed from the paper cassette 131 will be explained below.
When a pickup roller 132 makes one revolution, one of transfer sheets 112 on the multi-tray (paper cassette) 131 is fed to paper feed rollers 134. The transfer sheet 112 is fed to registration rollers 135 upon rotation of the paper feed rollers 134, and stands by for synchronization with an image forming unit.
A registration sensor 137 as a combination of a photointerrupter (light transmitting sensor) and flag processing is arranged in the vicinity of the registration rollers 135, and detects that the leading end of the transfer sheet 112 arrives the registration roller 135.
An image forming apparatus control circuit 402 (FIG. 14) that controls the image forming unit detects the arrival timing of the leading end of the transfer sheet 112 to the registration rollers 135 on the basis of the detection result of the registration sensor 137, starts image formation on the photosensitive drum 108 and controls the temperature of a halogen heater (not shown) of a fixing unit 121 to a predetermined value.
The transfer sheet 112 which stands by at the position of the registration rollers 135 is conveyed in synchronism with the timing of the detection result of the registration sensor 137 and the image forming process, and a toner image formed on the photosensitive drum 108 is transferred onto the transfer sheet 112 by a transfer roller 120. The transfer sheet 112 on which the toner image has been transferred is fixed by the fixing unit 121 which incorporates a halogen heater, and is guided to an discharge unit 122 as the upper portion of the image forming apparatus via discharge rollers 140 and a flapper 141 set at the a side, and is discharged from the discharge unit 122 by discharge rollers 156.
On the other hand, a sheet processing apparatus 302 is connected as an option to the image forming apparatus 301, and the following control is made to discharge a sheet to the sheet processing apparatus 302.
When the sheet processing apparatus 302 is connected to the image forming apparatus 301 and a connected host computer or the like (not shown) issues an discharge instruction to the sheet processing apparatus, the image forming apparatus control circuit 402 sets the flapper 141 to the b side, and conveys the transfer sheet 112 into the sheet processing apparatus 302 by the discharge rollers 140 after the printed transfer sheet 112 has passed the fixing unit 121. The transfer sheet 112 that has undergone image formation by the image forming apparatus main body 301 is passed to the sheet processing apparatus 302 connected as an option with its obverse surface facing up (face up).
As shown in FIG. 14, a sheet processing apparatus control circuit 409 in the sheet processing apparatus 302 is connected to the image forming apparatus control circuit 402 in the image forming apparatus main body to communicate with each other. When the image forming apparatus control circuit 402 issues a staple instruction for stapling a set of a plurality of transfer sheets, the sheet processing apparatus control circuit 409 conveys the transfer sheet 112 to a stack tray used to staple it intact or while being reversed by a reverse mechanism in a stacker. The transfer sheet 112 conveyed to the stack tray is aligned in the convey direction and widthwise direction by an aligning plate until a predetermined number of transfer sheets 112 are conveyed. When a set of a predetermined number of transfer sheets is formed, a shutter is closed to fix and staple the set of transfer sheets.
The set of transfer sheets 112 stapled by the stapler is discharged onto the discharge tray by driving discharge rollers.
The staple operation in the sheet processing apparatus 302 will be described below mainly with reference to FIGS. 12 to 14.
Reference numeral 303 denotes an entrance sensor which detects the transfer sheet 112 fed from the image forming apparatus main body 301. The detection information of the transfer sheet 112 by the entrance sensor 303 is input to the sheet processing apparatus control circuit 409. Upon reception of this information, the sheet processing apparatus control circuit 409 drives a transfer sheet convey motor (not shown). When the transfer sheet convey motor is driven, entrance rollers 304, reverse rollers 310, a slip roller 306, and a pair of set convey rollers (set convey means) 305 are simultaneously driven.
The reverse rollers 309 are initially rotated to convey the transfer sheet 112 in the feed direction. However, when a reverse solenoid works in response to a signal output from the sheet processing apparatus control circuit 409, the rotation direction of the rollers 309 is reversed to convey the transfer sheet 112 in the reverse direction. Reference numeral 308 denotes a flapper which is controlled by the sheet processing apparatus control circuit 409. When a flapper solenoid (not shown) operates, the transfer sheet 112 is fed into the convey rollers 310 facing up, and forms a transfer sheet set 112a on a stack tray (stack means) 318.
The pair of convey rollers 305 normally contact the convey path surface. When a set convey roller solenoid (not shown) controlled by the sheet processing apparatus control circuit 409 is driven, the upper roller of the rollers 305 moves upward to a set convey roller upper position 305a where that roller does not contact the convey path surface. While the set convey roller solenoid is driven, a shutter 307 is closed.
When the transfer sheets 112 are stacked on the stack tray 318 to staple the transfer sheet set 112a, the set convey roller solenoid is driven to move the upper one of the set convey rollers to the position 305a, and to close the shutter 307.
The slip roller 306 has a very weak convey force. The roller 306 conveys the sheet until the leading end of the sheet contacts the shutter 307, and slips on the sheet so as to align the sheet leading end and to hold the sheet position after the sheet leading end contacts the shutter 307. When the transfer sheet 112 begins to be stacked, a stack tray sheet sensor 313 detects the sheet and inputs a detection signal to the sheet processing apparatus control circuit 409. An alignment means that aligns the leading end portions of the transfer sheets 112 is formed.
When the transfer sheets 112 are to be stacked at the position of the shutter 307, aligning plates R 402 and L 403 are moved in the widthwise direction in correspondence with the size of the transfer sheets 112. The aligning plates R 402 and L 403 are controlled by the sheet processing apparatus control circuit 409 via an aligning plate motor drive circuit (not shown) and are driven by aligning plate R and L motors (neither are shown).
The moving positions of the aligning plates R 402 and L 403 are controlled by determining moving amounts from aligning plate R and L home position sensors (not shown) by the sheet processing apparatus control circuit 409 on the basis of the transfer sheet size which is sent from the image forming apparatus control circuit 402 via a communication line.
When a predetermined number of transfer sheets 112 are stacked, the image forming apparatus control circuit 402 issues a staple designation to the sheet processing apparatus control circuit 409. Upon reception of the staple designation, the sheet processing apparatus control circuit 409 moves a staple unit 312 in the widthwise direction indicated by the double-headed arrows, and drives a staple motor (not shown) in a staple drive unit 410, thus stapling the transfer sheet set 112a. The staple unit 312 is moved by driving a stapler moving motor (not shown) controlled by the sheet processing apparatus control circuit 409. The moving amount of the staple unit 312 is controlled by the sheet processing apparatus control circuit 409 on the basis of the moving distance from a stapler unit home position sensor (not shown).
Whether or not the operation of a stapler 312a of the staple unit 312 normally ends can be confirmed when a staple cam returns to the position of the staple home position sensor a predetermined period of time after the sheet processing apparatus control circuit 409 begins to drive the staple motor. When the shutter 307 is opened before the transfer sheet set 112a is stapled, and the transfer sheet set 112a is stapled after it is conveyed by a predetermined distance, the transfer sheet set 112a can be stapled at an arbitrary position in the convey direction.
A pair of discharge rollers (set discharge means) R 406 and L 407 are arranged near downstream of the shutter 307. Reference numeral 317 denotes an discharge sensor which is equipped on an discharge tray (sheet set stack means) 316, and inputs a sensor signal to the sheet processing apparatus control circuit 409.
In the conventional image forming apparatus 301 and sheet processing apparatus 302 as an option, a power supply circuit 401 for the image forming apparatus and a power supply circuit 415 for the sheet processing apparatus are independently provided, and are connected to a commercial power supply via AC plugs 411 and 414, thus operating the image forming apparatus 301 and sheet processing apparatus 302.
The reason why commercial power is supplied to the respective power supply circuits is that the sheet processing apparatus 302 requires large power in the staple operation, as shown in FIG. 15, and it is not practical to design the power supply circuit 401 for the image forming apparatus main body 301 as a large-capacity power supply circuit in consideration of the load on the sheet processing apparatus 302.
In FIG. 15, a current Is1 that requires normal operations such as a sheet convey operation and the like of the sheet processing apparatus is as relatively small as about 24 V/1 A. However, when the staple operation is done, a maximum current Is3 as high as 5 A flows for about 100 msec. In order to supply electric power from the image forming apparatus to the sheet processing apparatus in consideration of electric power based on this maximum current Is3, the output electric power of the power supply for the image forming apparatus must be set as high as about 120 W(=24 V×5 A). As a result, a large-scale, expensive power supply circuit is required, resulting in an increase in price which is unnecessary for users who use only the image forming apparatus (does not require any sheet processing apparatus).
For this reason, conventionally, since the power supply circuit 401 for the image forming apparatus 301 and the power supply circuit 415 for the sheet processing apparatus 302 are independently provided, minimum required portions (e.g., a communication interface and the like) are provided to the image forming apparatus main body for the sheet processing apparatus as an option, thus suppressing an increase in cost.
On the other hand, as one of reasons why the power supply circuits are independently provided, an image forming apparatus that requires a sheet processing apparatus is normally limited to a large-scale, high value-added image forming apparatus such as a monochrome high-speed printing machine, a high image quality machine that can perform color print, and the like.
More specifically, the power supply circuits are independently provided for the following reasons: two AC plugs are agreeable in terms of design since a system formed by connecting the image forming apparatus to the sheet processing apparatus as an option is bulky; even when the total AC current that flows in the system of the image forming apparatus and sheet processing apparatus exceeds maximum allowable electric power (e.g., 1,500 W) of one commercial power supply system, since the system is installed by a service person, the service person need only connect the two AC plugs to different commercial power supply systems so as not to exceed the maximum allowable electric power of the commercial power supply; and so forth.
In recent years, along with the improvements of the technologies of image forming apparatuses, image forming apparatuses which belong to a category of middle-speed machines (middle-class machines) have been speeded up while their size and price reductions are achieved, and have gained a speed comparable to that of conventional high-speed machines. Based on such improvements, added values such as expandability of options, energy savings, and the like are demanded from the market more strongly.
Under such circumstances, a demand is increasing for an image forming apparatus which can improve its design upon mounting an option and allows the user to easily attach/detach an option by supplying electric power from the image forming apparatus to an option apparatus.
However, when electric power is supplied from the power supply in the image forming apparatus main body to the sheet processing apparatus such as a staple stacker or the like, the staple operation requires large electric power, as described above. For this reason, a large-capacity power supply circuit must be prepared in the image forming apparatus main body in consideration of consumption power in the sheet processing apparatus. However, this arrangement results in an increase in price unnecessary for users who use only the image forming apparatus. In order to meet such conflicting requisites, it is demanded to reduce electric power to be supplied to the sheet processing apparatus and to minimize an increase in cost of the image forming apparatus main body.
In a large-scale, high value-added image forming apparatus such as a monochrome high-speed printing machine, a high image quality machine that can perform color print, and the like, i.e., in a so-called high-speed machine (high-class machine), more functions are required, and consumption power tends to increase although energy-saving measures are taken. One indication of the upper limit of electric power consumed by these apparatuses is the maximum electric power (e.g., 1,500 W=100 V×15 A if the commercial power supply voltage is 100 V) that can be supplied by the commercial power supply.
In general, the image forming apparatus main body is normally designed so that the maximum electric power of the apparatus does not exceed that of the commercial power supply. Therefore, when an option such as the sheet processing apparatus that consumes relatively large electric power or the like is connected to the image forming apparatus whose maximum electric power is approximate to that of the commercial power supply, it is recommended that a power supply circuit is independently provided to the sheet processing apparatus, and is connected to a commercial power supply system different from the main body using an AC plug different from the image forming apparatus main body.
However, the AC plugs of the image forming apparatus main body and sheet processing apparatus are often connected to the same commercial power supply system unless they are connected by a service person or the like in consideration of the maximum consumption power. Therefore, it is demanded to reduce the maximum electric power of each of the image forming apparatus and sheet processing apparatus so as to prevent protection means such as the circuit breaker of the commercial power supply from operating even when the two AC plugs are connected to the same commercial power supply system, and to prevent the maximum electric power of the system from exceeding the maximum electric power that can be supplied by one commercial power supply system.